Intertwined orbital distribution of charge density waves in NbSe 2

Charge density wave (CDW) resulting from a periodic distortion in the lattice creates orders beyond the original lattice. In <a:math xmlns:a="http://www.w3.org/1998/Math/MathML"> <a:mrow> <a:mn>2</a:mn> <a:msub> <a:mrow> <a:mi>H</a:mi> <a:mtext>−</a:mtext> <a:mi>NbSe</a:mi> </a:mrow> <a:mn>2</a:mn> </a:msub> </a:mrow> </a:math> , one of the layered transition metal dichalcogenides, the <b:math xmlns:b="http://www.w3.org/1998/Math/MathML"> <b:mrow> <b:mn>3</b:mn> <b:mo>×</b:mo> <b:mn>3</b:mn> </b:mrow> </b:math> charge order appears in two-dimensional (2D) layers. Although CDW can be observed by different techniques, the spatial distribution within a 2D layer has never been systematically visualized. Here, by using scanning tunneling microscopy and density functional theory, we monitored the evolution of CDW along the <c:math xmlns:c="http://www.w3.org/1998/Math/MathML"> <c:mi>c</c:mi> </c:math> axis and found a strong relation with the orbital charges. The results show that the appearance of the CDW varies while tuning the tunneling current and undergoes a transition from Se orbital charges to Nb orbital charges. The calculation of orbital charge distributions shows that both CDW intensity modulation and the transition are strongly intertwined with the distribution of Se <d:math xmlns:d="http://www.w3.org/1998/Math/MathML"> <d:mrow> <d:mn>4</d:mn> <d:mi>p</d:mi> </d:mrow> </d:math> orbitals and Nb <e:math xmlns:e="http://www.w3.org/1998/Math/MathML"> <e:mrow> <e:mn>4</e:mn> <e:mi>d</e:mi> </e:mrow> </e:math> orbitals.